A joint within the human body forms a juncture between two or more bones or other skeletal parts. The ankle, hip, knee, shoulder, elbow and wrist are just a few examples of the multitude of joints found within the body. As should be apparent from the above list of examples of joints, many of the joints permit relative motion between the bones. For example, the motion of sliding, gliding, hinge or ball and socket movements may be had by a joint. For example, the ankle permits a hinge movement, the knee allows for a combination of gliding and hinge movements and the shoulder and hip permit movement through a ball and socket arrangement.
The joints in the body are stressed or can be damaged in a variety of ways. For example, the gradual wear and tear is imposed on the joints through the continuous use of a joint over the years. The joints that permit motion have cartilage positioned between the bones providing lubrication to the motion and also absorbing some of the forces direct to the joint. Over time, the normal use of a joint may wear down the cartilage and bring the moving bones in a direct contact with each other. In contrast, in normal use, a trauma to a joint, such as the delivery of a large force, from an accident, for example, an automobile accident, may cause considerable damage to the bones, the cartilage or to other connective tissue such as tendons or ligaments.
Arthropathy, a term referring to a disease of the joint, is another way in which a joint may become damaged. Perhaps the best known joint disease is arthritis, which is generally referred to a disease or inflammation of a joint that results in pain, swelling, stiffness, instability, and often deformity.
There are many different forms of arthritis, with osteoarthritis being the most common and resulting from the wear and tear of a cartilage within a joint. Another type of arthritis is osteonecrosis, which is caused by the death of a part of the bone due to loss of blood supply. Other types of arthritis are caused by trauma to the joint while others, such as rheumatoid arthritis, Lupus, and psoriatic arthritis destroy cartilage and are associated with the inflammation of the joint lining.
The hip joint is one of the joints that is commonly afflicted with arthropathy. The hip joint is a ball and socket joint that joins the femur or thigh bone with the pelvis. The pelvis has a semispherical socket called the acetabulum for receiving a ball socket head in the femur. Both the head of the femur and the acetabulum are coated with cartilage for allowing the femur to move easily within the pelvis. Other joints commonly afflicted with arthropathy include the spine, knee, shoulder, carpals, metacarpals, and phalanges of the hand. Arthroplasty as opposed to arthropathy commonly refers to the making of a artificial joint. In severe cases of arthritis or other forms of arthropathy, such as when pain is overwhelming or when a joint has a limited range of mobility, a partial or total replacement of the joint within an artificial joint may be justified. The procedure for replacing the joint varies, of course, with the particular joint in question, but in general involves replacing a terminal portion of an afflicted bone with a prosthetic implant and inserting a member to serve as a substitute for the cartilage.
The prosthetic implant is formed of a rigid material that becomes bonded with the bone and provides strength and rigidity to the joint and the cartilage substitute members chosen to provide lubrication to the joint and to absorb some of the compressive forces. Suitable material for the implant include metals, and composite materials such as titanium, cobalt chromium, stainless steel, ceramic and suitable materials for cartilage substitutes include polyethylene. A cement may also be used to secure the prosthetic implant to the host bone.
A total hip replacement, for example, involves removing the ball shaped head of the femur and inserting a stem implant into the center of the bone which is referred to as the medullary canal or marrow of the bone. The stem implant may be cemented into the medullary canal or may have a porous coated surface for allowing the bone to heal directly to the implant. The stem implant has a neck and a ball shaped head which are intended to perform the same functions as a healthy femur's neck and a ball shaped head. The polyethylene cup is inserted into the acetabulum and has a socket for receiving the head on the stem implant.
Unfortunately, some patients who have undergone partial or total joint replacements require revision surgery. Revision surgery may be required soon after the primary surgery or may not be needed for years. Revision surgery may be required for one of a number of reasons. For one, fixation of the joint may be compromised. A trauma of to the joint may result in the loosening or the loosening of the joint may have been caused by other factors, such as an insufficient bond between the implant and the host bone. The loosening of an implant can be quite painful and also can pose danger to the patient. For example, movement of the loose implant within the bone may fracture the bone itself.
Revision surgery may be necessary for other reasons. For example, particle debris from the cartilage substitute member or even from any of the other implants may cause osteolysis in the patient. In general osteolysis is the body's natural immune response to foreign objects which result in inflammation and pain in the joint. Another reason why revision surgery may be necessary, is due to death of part of the bone. A bone requires stress in order to remain strong and any bone that is not stressed will become weak and fragile. This result is often known as Wolf's Law. The insertion of an implant may stress shield portions of the bone whereby these portions no longer receive the stress that it requires in order to remain strong. Another reason to perform revision surgery is to take advantage of advancements in prosthetic design. Thus, for many reasons, revision surgery may be necessary or desirable for a patient.
Revision surgery is more complicated than the primary partial or total joint replacements since it requires removal of the previously inserted stem implant and introduction of another stem implant. When the stem implant is removed, a portion of the surrounding tissue is removed along with the implant. If cement was used to secure the original implant, then additional tissue is normally removed to insure that all the cement has been removed from within the medullary canal. When cement is not used, often a porous surface is formed on the implant to promote bony ingrowth. This area around the bony ingrowth may need to be removed and may require tools to separate the prosthesis from the bone. During a revision surgery, this void left by the removal of the surrounding tissue must be filled in order to allow the stem implant to bond with the host bone.
Surgical techniques have been developed for the revision of the hip system. In these prior arts systems, bone may be harvested from another portion of the patient to form an autograft which may be tamped in positioned in the bone cavity, for example the femur. Alternatively, substitute bone material may be used. Such bone material may be an allograft or human tissue available from a tissue bank or may be artificial tissue obtained from Pro Osteon™ available from Interpore, 181 Technology Drive, Irvine, Calif. A small portion of the autograft, the allograft, or the artificial bone material is bone is inserted into the femur and packed and the process is repeated until a portion of the femur has been filled.
A tamping process may be performed which packs material into the medullary canal until the bone cavity is the proper size for the stem implant. This process may include the use of progressively large tamps until a tamp representing the size and shape of the implant's stem is used.
After the packing of the canal is complete, blood pooled at the distal end of the stem may be extracted with suction applied in the tamp. The tamp is then removed just immediately prior to the insertion of the cement into the canal. A cement gun with a nozzle cut off to the length of the stem is use to inject cement into the narrow distal stem area. A second, larger nozzle may then be used to complete the filling of the proximal femur and to pressurize the cement. The stem is inserted and the pressure maintained until the cement has polymerized.
This method is wrought with several problems. One of these problems is that in order to tamp the morselized bone into the cavity, the distal portion of the cavity must first be filled and a large quantity of graft material must be used. It may be traumatic for the patient as additional morselized bone must be harvested from the patient. Conversely, when bone substitute material issues, a larger and more expensive amount of material must be used. Further the packing of the entire canal may cause additional blood loss and blood flow as the blood is absorbed and moved toward the open portion of the cavity as the material continues to be packed by the tamps.
Further, the use of the tamps create a limit on the shape of the cavity created by the tamp as well as limiting the precision of the fit of the tamp to the prosthesis stem.
The present invention is aimed at alleviating at least some of the aforementioned problems.